Iridium-tungsten alloy products



United States Patent 3,262,779 IRIDiUM-TUNGSTEN ALLOY PRDDUCTS Edward George Price, Chiswick, London, and Laszlo Dezso Romhanyi, Kingston-upon-Thames, Surrey, England, assiguors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 5, 1963, Ser. No. 321,439

Claims priority, application Great Britain, Nov. 8, 1962, 42,273/ 62 3 Claims. (Cl. 75-172) The present invention relates to resilient metal products and, more particularly, to heat-resistant resilient metal products containing iridium and tungsten.

It is well known that springs are used for storing elastic strain energy. Elastic strain energy is work done in deforming a body within the elastic limit of the material of the body. Springs are resilient elements, frequently of metal, and in many instances are known by their structure, for instance, helical springs, coned disk (Belleville) springs, flat spiral springs, etc. Springs are also known by their function, one definition (which is adopted herein) of an ideal spring being-an elastic body whose primary iunction is to deflect or distort under load and to recover its original shape when released after being distorted. Although most material bodies are elastic and will distort under load, they are not all considered springs. Thus, a structural steel beam will distort under load, but it is not considered as a spring because its primary -function is not to deflect under load but rather to remain rigid.

An important property of a spring is low relaxation value. If a spring on being released from load returns to its initial position, it has zero relaxation. If it does not return to the initial position, but only to some intermediate position, then the extent of its deflection, extension and/ or compression as the case may be, after it has been released can be expressed as a percentage of the deflection under load, and is the relaxation value. The relaxation value rapidly increases with temperature and it also increases with the time during which the spring is under load at elevated temperature.

Some springs have to be used at elevated temperatures and certain nickel-cobalt-chromium alloys are very satisfactory for use in the temperature range of 300 C. to 500 C. At temperatures above this and up to 800 0, these alloys are not very satisfactory, particularly because at temperatures above 500 C. the relaxation value of springs of these alloys is undesirably high.

Although many attempts were made to overcome the foregoing difiiculties and other disadvantages, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

Alloys of iridium and tungsten are known, being described in a paper by Raub and Walter in Festschrift aus Anlass des 100-jahrigen Jubilaums der Firma, W. C. Heraeus, G.m.b.H. It has now been discovered that iridium-tungsten alloys of a critical composition have characteristics which render them extremely suitable as materials for springs.

It is an object of the present invention to provide a wrought iridium-tungsten alloy specially adapted for use as spring material.

Another object of the invention is to provide Wrought iridium-tungsten alloy products such as wire, bar, sheet, strip and the like for manufacture into resilient members.

The invention also contemplates providing springs having low relaxation value and high oxidation resistance at temperatures of 600 C. and higher.

It is likewise within the contemplation of the invention Patented July 26, 106$ to provide, as a new use, a process wherein an iridiumtungsten alloy is used as a spring.

Generally speaking, the present invention contemplates a wrought alloy consisting of about 0.5% to about 7% tungsten and the balance essentially iridium, i.e., at least about 93% of the alloy is iridium. The invention also contemplates wrought products and resilient elements of the aforedescribed alloy of the invention and further contemplates use of this alloy as a resilient element such as a spring. Springs made of wrought alloys of the invention possess high resistance to relaxation, i.e., have low relaxation. values, at temperatures of at least about 600 C. and even higher and are highly resistant to oxidation at such temperatures.

According to the invention, springs are made of alloys of iridium and tungsten containing from 0.5% to 7% tungsten, the balance being substantially all iridium. IA. discovery of the invention is that these alloys have distinctly lower relaxation values at high temperatures than the alloys at present in use. For example, the relaxation value of a spring loaded to a maximum stress of 20,000 pounds per square inch (p.s.i.) after 200 hours at 700 C. when made of a wrought alloy consisting of 5% tungsten and 95% iridium is less than 20%, and that of a Wrought alloy consisting of 2% tungsten and 98% iridium is less than 40%, whereas the nickel-cob alt-chromium alloys (which alloys contain 15% to 21% cobalt, 18% to 21% chromium, 1.8% to 3% titanium, 0.8% to 2% aluminum, up to 5% iron with the balance nickel) commonly used have under the same stress a relaxation value of or more. At 600 C. the advantage of the 5% tungsten alloy is also (though less) pronounced, the relaxation being still under 20% after 500 hours, whereas that of the nickelco balt-ohromium alloy is 40% after 500 hours.

The alloy of the invention must contain at least about 0.5 tungsten in order for the alloy to be characterized by a high limit of proportionality, a high temperature of recrystallization and to possess good relaxation properties. The tungsten content must not be greater than about 7% because otherwise the alloys are not able to be fabricated into forms suitable for use as spring components. When it is stated that the balance is essentially iridium, it is to be understood that the balance will be substantially all iridium but can contain small amounts of other elements which do not aifect the basic character of the alloy or its behavior in use. The total amount of all elements other than iridium and tungsten is very small, i.e., about 0.5 or less. Now, iridium usually contains small amounts of other precious metals such as gold, platinum, palladium, ruthenium, rhodium, silver and osrnium in a total amount of up to about 0.2% or less. Molybdenum in small amounts, e.g., up to about 0.1%, may be associated with tungsten in the alloy. The balance may also include up to about 0.1% of iron, up to about 0.1% of copper and up to about 0.1% nickel.

A further advantage of the alloys used according to the invention is that good electrical contact can easily be made on them. For many electrical purposes springs are not only required to work at high temperature but they are also expected to be good conductors of electricity and make good contact with a complementary current carrying component. The nickel-cobalt-chromium alloys form oxides at temperatures above 300 C. and these oxides inhibit good electrical contact. N 0 similar oxides are formed on the alloys of the invention.

The sprin s according to the invention can be made by starting with a mixture of iridium and tungsten powders, melting this mixture under an argon arc to produce an ingot and hot working the ingot to strip or wire. The springs can be in blade or coil form, coiling preferably 3 being effected in the temperature range of 650 C. to 700 C.

In carrying the invention into practice, it is advantageous that the tungsten content of the wrought alloys of the invention be about 3% to about 6% in order to provide good spring properties commensurate with the workability of the alloy into spring components.

For the purpose of giving those skilled in the art a better understanding and appreciation of the advantages of the invention, the following illustrative examples are given. Wrought iridium-tungsten alloys of the chemical compositions set forth in Table I were produced by melting and casting the alloys into ingots. The ignots were hot forged at 1200 C. to 1500 C. and then hot drawn at 600 C. to 800 C. to wire. Alloys 1, 2 and 3 are examples of iridium-tungsten alloys in accordance with the invention. Alloy Xis a nickel-cobalt-ch'romium alloy which has been used for heat-resistant springs in the prior art. All chemical compositions set forth herein are in weight percentages and the level of impurities in alloys 1, 2 and 3 is well within the limits specified in the foregoing for alloys in accordance with the invention.

TAB LE I Alloy Percent Percent Percent Percent Percent Balance W Cr Al Tl Iridium 1s 20 2 3 Nickel.

TABLE II Ultimate Tensile Strength at Room Temperature, p.s.i.

Modulus of Elasticity at Room Temperature, p.s.i.

Recrystallization Tempera- Alloy ture, C.

As shown in Table II, wrought alloys which contain about 0.5% to about 7% tungsten and which are in accordance with the invention are characterized by recrystallization temperatures of 900 C. and higher, and moduli of elasticity of 76 million p.s.i. and higher. Also, as shown in Table II, alloys of the invention possess ultimate tensile strengths of 300,000 p.s.i. and more. Further, the very high tensile strength of 380,000 p.s.i. is achieved when the tungsten content of an alloy of the invention is in the advantageous range of 3% to about 6%.

Springs made of alloys 1, 2, 3 and X were tested for relaxation at elevated temperature by stressing cantilever springs of 0.02" wire to a maximum stress of 20,000 p.s.i. in a high temperature zone at the temperatures set forth in Table III. Results of these tests are set forth in Table HI.

TABLE III Percentage Relaxation in 100 Hours Alloy 600 C. 700 C. 800 C.

25 100 (fully relaxed).

of elasticity and recrystallization temperatures and low relaxation values of these wrought alloys.

The present invention is particularly applicable to processes of resiliently storing energy by deforming, deflecting and/ or otherwise straining elastic bodies, usually within the elastic limit of the material of the body.

Thus, the invention provides processes wherein resilient elements made of Wrought alloys of the invention, which alloys contain about 0.5 to about 7% tungsten with the balance substantially iridium, are used as springs. By virtue of the low relaxation values of springs of the invention, losses of stored energy are minimized when alloys of the invention are used as springs at elevated temperatures. The invention is also applicable to processes of elastically supporting and/or restraining structural members where the supporting or restraining means are exposed to elevated temperatures. When such supporting or restraining is performed using alloys of the invention as springs, advantages of dimensional stability of the combination of supporting or restraining means and structural members are achieved. Springs which can be produced in accordance with the invention include helical springs, fiat spiral springs, coned disk (Belleville) springs, leaf springs, wire springs, torsion springs, tension springs, etc., and are useful in any device where springs are required to operate at elevated temperature, such as high temperature micro switches and thermocoupled contact springs for fuel-can temperature control.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. Wrought resilient iridium-tungsten alloy sheet, strip, wire, bar and like products especially adapted for manufacture into resilient articles consisting of 0.5 to 7% tungsten with the balance essentially iridium and characterized by a modulus of elasticity of at least 76 million pounds per square inch, an ultimate tensile strength of at least 300,000 pounds per square inch and a recrystallization temperature of at least 900 C.

2. A wrought resilient iridium-tungsten alloy product as set forth in claim 1 wherein the tungsten content is 3% to 6%.

3. A wrought resilient article made of an alloy consisting essentially of 0.5 to 7% tungsten with balance essentially iridium, said article being characterized by low relaxation when elastically deflected under load at temperatures of up to 600 C. and higher, together with good electrical contact characteristics.

References Cited by the Examiner Hansen, Constitution of Binary Alloys, 2nd Edition, 1958, page 875. Published by McGraw-Hill Book Company, New York, N.Y.

DAVID L. RECK, Primary Examiner.

R. O. DEAN, H. F. SAITO, Assistant Examiners. 

1. WROUGHT RESILIENT IRIDIUM-TUNGSTEN ALLOY SHEET, STRIP, WIRE, BAR AND LIKE PRODUCTS ESPECTIALLY ADPATED FOR MANUFACTURE INTO RESILIENT ARTICLES CONSISTING OF 0.5% TO 7% TUNGSTEN WITH THE BALANCE ESSENTIALLY IRIDIUM AND CHARACTERIZED BY A MODULUS OF ELASTICITY OF AT LEAST 76 MILLION POUNDS PER SQUARE INCH, AN ULTIMATE TENSILE STRENGTH OF AT LEAST 300,000 POUNDS PER SQUARE INCH AND A RECRYSTALLIZATION TEMPERATURE OF AT LEAST 900*C. 